1. Field of the Invention
The present invention relates to a fuel cell system having a fuel cell.
2. Description of the Related Art
A fuel cell generally generates electrical energy by using hydrogen and oxygen as fuels. Because of its superiority in terms of the environment and ability to achieve high energy efficiency, development is being widely conducted into the use of fuel cells as future energy supplying systems.
At present, in many fuel cells, a reformed gas that contains hydrogen is generated from a hydrocarbon-based fuel such as gasoline, natural gas, or methanol, using a reformer, and the generated reformed gas is supplied to an anode of the fuel cell. In the reformer, reforming is performed by, for example, a steam reforming reaction that uses steam.
Because the steam reforming reaction is an endothermic reaction, the reformer is heated to promote the reforming reaction. For this reason, fuel cell systems are developed in which heat is provided to the reformer using a combustor or the like. For example, Japanese Patent Application Publication No. JP-A-2005-235583 describes an art using anode off-gas as fuel gas for heating the reformer. According to this art, a high reforming efficiency is achieved.
However, because the ratio of methane contained in the reformed gas changes, depending upon the conditions within the reformer, the ratio of methane in the anode off-gas also changes. Because methane is difficult to combust, a temperature distribution might occur inside the reformer. As a result, the combustor may not generate sufficient heat.